Conditional Routing Technique

ABSTRACT

A technique for controlling network routing in a network ( 100 ) is provided. The network ( 100 ) includes a first end node ( 102 ) and a second end note ( 104 ). The end nodes are connectable along a first routing path ( 106 ) by at least one link ( 113 ). The network ( 100 ) further provides a second routing path ( 108 ) including the first end node ( 102 ) and the second end nodes ( 104 ). As to a method aspect of the technique, one or more queues ( 402 ) are provided. Each of the queues ( 402 ) serves at least one tunnel (Tunnel —   1;  Tunnel —   2 ) along the first routing path ( 106 ). A switching of the tunnel (Tunnel —   1 ) to the second routing path ( 108 ) is triggered based on a combination of two pieces of information. A piece of information includes information as to a queue build-up at the queue ( 504 ) serving the tunnel (Tunnel —   1 ). Another piece of information includes information as to a capacity of the link ( 113 ) of the first routing path ( 106 ).

TECHNICAL FIELD

The present disclosure generally relates to a technique for controllingdata flow in a network and to network components thereof. In particular,and without limitation, the disclosure relates to a technique thatdetermines conditions for rerouting the data flow.

BACKGROUND

Modern communication networks carry a plurality of different services,such as voice and data services. From a technical point of view, therole taken by the network, or a sub-network thereof, in carryingservices can be considered as providing a network connection, whereinrequirements as to availability and capacity of the network connectionoften depend on the type of service. Availability refers to the degreeto which the network connection is in a specified state of operationsuitable for the service, such as the existence of network connectivityat a specified capacity. Capacity refers to the data rate provided bythe network connection. The actual physical routing path used in thenetwork for providing the network connection is often subordinate forthe service at an application layer and should be transparent to a user.

Adaptive Modulation (AM) applied to a link in the network, e.g., a linkusing microwave equipment, is an efficient tool to increase the capacityof the link. There is often a trade-off between availability andcapacity. For example, a microwave link is planned for a small Bit ErrorRate (BER) at a basic modulation level applied during a major part ofits operation time, which results in approximately 99.999% availabilityof the link. Adaptive modulation means that in good radio conditions,the microwave channel is able to provide significantly higher capacityusing higher modulation levels with lower availability. For example, theavailability can decrease from 99.995% to 99.9% the higher themodulation level. A currently used modulation level thus depends oncurrent radio channel conditions, such as a Signal-to-Noise Ratio (SNR).The automatic changing between modulation levels according to AMprovides the highest available link capacity given the current radiochannel conditions.

Different types of services have different Quality of Service (QoS)requirements including a minimum capacity and a maximum time of outage.In a double-connected network, for example using microwave links, it ispossible to protect the services carried by the basic modulation levelby a protection switching mechanism. When the link capacity is goingdown to zero, the protected traffic is rerouted to an alternative path,which does not contain the failed link. Herein, “failed” and “fault”refer to the outage of network connectivity. The Recommendation ITU-TG.8031/Y.1342 defines an examples of the protection switching mechanismin the context of Ethernet Operation, Administration and Maintenance(OAM). For example, in the context of voice telecommunication, servicescan tolerate only a short time of outage. Consequently, the rerouting,which is also referred to as switching, should be completed within alimited restoration time, for example within 50 ms.

Conventional protection switching mechanisms only detect the loss ofconnectivity, for example, because continuity check messages with highpriority are used to probe the connectivity. A reduction in linkcapacity to an insufficient but non-zero capacity, for example due toAM, is not detected, although the service is already affected or evenhas collapses as a consequence of the insufficient reduced linkcapacity.

Other conventional techniques reroute services when it is not evennecessary. When the link capacity is degraded, a predefined reroutingcan be performed by default for some demands. However, if the actualtraffic volume of a service is less than the degraded link capacity,rerouting is unnecessary and would add a futile workload for thenetwork.

A possible solution for avoiding unnecessary service rerouting couldbase the rerouting decision on a measurement of both the actual trafficvolume needed for the service and the actual link capacity available tothe service. However, such measurements and their subsequent analysistake too long to fulfill the limited restoration time. Furthermore, themeasurements require additional hardware equipment and software.Moreover, the measurements cause additional network traffic.

SUMMARY

Accordingly, there is a need for a technique that more accurately routesservices in a network in compliance with certain quality of servicerequirements.

According to one aspect, a method of controlling network routing in anetwork includes the step of triggering a protection switching based onthe combination of current link capacity information and queue build-upinformation.

According to another aspect, a method of controlling network routing ina network is provided. The network includes a first end node and asecond end node connectable along a first routing path via at least onelink. The network further provides a second routing path including thefirst end node and the second end node. The method comprises the stepsof providing one or more queues, each of which serves at least onetunnel along the first routing path; and triggering a switching of atleast a portion of the at least one tunnel to the second routing pathbased on a combination of information as to a queue build-up at thequeue serving the tunnel and information as to a link capacity of atleast one of the links of the first routing path.

The expression “queue build-up” of a queue may encompass at least one ofa certain level of aggregation of data by the queue, a certain increaseof data aggregated by the queue and a certain rate at which data isaggregated by the queue. The triggering may depend on a combination ofthe queue build-up information and the link capacity information. Thecombination may be a logical conjunction.

At least in some embodiments, a more accurate switching decision can beachieved based on the combined information. In same or some otherembodiments, accounting for the queue build-up at the queue serving thetunnel can prevent an unnecessary switching of the tunnel. Combining theinformation as to the queue build-up (also referred to as queue build-upinformation) with the information as to the link capacity (also referredto as link capacity information) allows at least some embodiments toexplicitly or implicitly differentiate between a case of capacitydegradation affecting the tunnel and a case of traffic overload of thetunnel. Some implementations of the technique may obviate a measurementof the actual capacity needed by the tunnel or may avoid a computationof remaining capacity headroom for the tunnel.

The tunnels served by the same queue may have the same Quality ofService (QoS) requirements. Not necessarily all tunnels that aresupported by the same queue are rerouted. Only complete tunnels may bererouted.

The link capacity information may indicate a reduction in the linkcapacity, e.g., due to a change in a modulation level applied to thelink. The link capacity information may be provided by the link.

The queue build-up information may indicate a queue length of the queueserving the tunnel. The queue build-up information may be obtained bychecking the queue length. The queue length may be checked bycontinuously or periodically monitoring the queue length. Indicating orchecking the queue length may encompass determining the queue length orcomparing the queue length.

A queue threshold may be set for each of the one or more queues. Theswitching of the tunnel may be triggered, if the queue length of thequeue serving the tunnel exceeds the respective queue threshold. Thequeue build-up information may include a result of a comparison betweenthe queue length and the queue threshold.

The queue length may represent an amount of data currently stored in thequeue for the tunnel. The queue build-up information may be indicativeof the queue length or its relation to the queue threshold. The queuelength exceeding the queue threshold may indicate the queue build-up.The queue length of the queue exceeding the respective queue thresholdof the queue may indicate the queue build-up at the queue.

The switching may be triggered during a case of reduced link capacity ofthe at least one of the links of the first routing path. The linkcapacity information may indicate the case of reduced link capacityand/or may quantify the reduction in link capacity. The reduced linkcapacity may be transient. The link capacity information may indicate atransient case of link capacity reduction or a current state of the atleast one of the links. The queue build-up may be checked periodicallyor continuously while the link capacity remains reduced. Alternativelyor in combination, the reduction in the link capacity may be checked ormonitored while the queue build-up is indicated, e.g., by the queuebuild-up information.

The triggering of the switching may be based on the occurrence of boththe reduction in the link capacity and the queue build-up. The queue atwhich the queue build-up occurs may be upstream of the link at which thereduction in the link capacity occurs.

The network may include at least one intermediate node along the firstrouting path between the end nodes. The first routing path may includethe first and second end nodes, the at least one intermediate node andlinks between the nodes.

At least one of the queue build-up information and the link capacityinformation may be at least one of available, determined, gathered,received and generated by the intermediate node. In at least someimplementations, the individual queue build-up information and/or theindividual link capacity information is not necessarily available at theend nodes. The queue build-up information and the link capacityinformation may be combined at the intermediate node.

The intermediate node may trigger the switching by informing the endnode as to the switching of the tunnel. The end node may thus beinformed as to a result of the combination of the queue build-upinformation and the link capacity information. The intermediate node mayinform the end node explicitly, e.g., by transmitting a message, orimplicitly, e.g., by the absence of a message expected at the end node.The intermediate node may trigger the switching by generating a controlmessage. The control message may be provided to the end node.Alternatively or in addition, the intermediate node may trigger theswitching by dropping data frames including a continuity check message.The continuity check message may be communicated along the first routingpath, e.g., by periodically transmitting data frames including thecontinuity check message. The end node may be adapted to reroute thetunnel from the first routing path to the second routing path inresponse to the loss of certain continuity check messages.

The one or more queues may be associated to one of the at least oneintermediate node along the first routing path. For example, a pluralityof queues may be provided at the intermediate node. A scheduler of theintermediate node may control the plurality of queues. The scheduler mayfurther control a transmission using the at least one link of the firstrouting path.

Each of the at least one intermediate node along the first routing pathmay have access to information as to which of the tunnels is to beswitched in case of a given link capacity. For example, some or each ofthe at least one intermediate node along the first routing path mayinclude a table containing the information as to which of the tunnels isto be switched in case of a given link capacity. The table may associatea queue to a given tunnel. Alternatively or in combination, the tablemay associate a minimum link capacity to a given tunnel. Alternativelyor in combination, the table may associate the queue threshold to agiven tunnel.

Data frames belonging to a tunnel may include an identifier indicativeof the tunnel. The intermediate node may be adapted to read theidentifier. The intermediate node may be configured to determine, e.g.,based the identifier, at least one of the queue associated to thetunnel, the minimum link capacity associated to the tunnel and the queuethreshold associated to the tunnel.

The switching may be triggered in response to the occurrence of thequeue build-up and the reduction in link capacity. The switching may betriggered immediately when the information indicates the queue build-up.Alternatively, the switching may further be subject to the queuebuild-up remaining for a certain period of time. In someimplementations, the triggering of the switching may include starting atimer. The timer may be started in response to the occurrence of thequeue build-up and the reduction link capacity. The switching mayfurther be subject to the queue build-up remaining until the timerexpires. For example, the switching may further be subject to the queuelength remaining larger than the queue threshold until the timerexpires.

The switched tunnel may be switched back from the second routing path tothe first routing path when the link capacity fulfils the minimum linkcapacity and/or another switch-back link capacity for a certain periodof time. The switch-back link capacity may be higher than the minimumlink capacity. The minimum link capacity may be associated to theswitched tunnel. The switch-back link capacity may be associated to thelink, e.g., a maximum capacity of the link. The minimum link capacitymay be retrieved from the information as to which of the tunnels is tobe switched in case of a given link capacity. The minimum link capacitymay be retrieved from the table.

The at least one link along the first routing path, some other link orall links along the first routing path and/or the second routing pathmay include microwave equipment.

The network may be a telecommunications network. For example, thenetwork may be a telecommunications backhaul network. Thetelecommunications backhaul network may interconnect a public datanetwork and a radio access network.

According to still another aspect, a computer program product isprovided. The computer program product comprises code portions forperforming one or more of the steps of the method described herein, whenthe computer program product is executed on one or more computingdevices. The computer program product may be stored on acomputer-readable recording medium such as a permanent or re-writablememory. The computer program product may also be provided for downloadin one or more computer networks, such as the Internet, a cellulartelecommunications network or a wireless or wired Local Area Network(LAN).

As for a hardware aspect, a device for controlling network routing in anetwork is provided. The network includes a first end node and a secondend node connectable along a first routing path via at least one link.The network further provides a second routing path including the firstend node and the second end node. The device is adapted to provide oneor more queues, each of which serves at least one tunnel along the firstrouting path; and to trigger a switching of at least a portion of the atleast one tunnel to the second routing path based on a combination ofinformation as to a queue build-up at the queue serving the tunnel andinformation as to a link capacity of at least one of the links of thefirst routing path.

As for a further hardware aspect, a network is provided. The networkcomprises a first end node and a second end node connectable along afirst routing path via at least one link, wherein the network furtherprovides a second routing path including the first end node and thesecond end node; and a device for triggering network routing in thenetwork according to one or more of above-mentioned aspects.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, further details and advantages of the disclosure aredescribed with reference to exemplary embodiments illustrated in thedrawings, wherein

FIG. 1 schematically illustrates a telecommunications network as anexemplary environment for implementing the present disclosure;

FIG. 2 shows a flowchart of an embodiment of a method of controllingnetwork routing in the network of FIG. 1;

FIG. 3 illustrates two scenarios for controlling network routing;

FIG. 4 illustrates an exemplary intermediate node for performing themethod of FIG. 2 in the network of FIG. 1;

FIG. 5 illustrates an example of a plurality of queues controlled by aschedule in the intermediate node of FIG. 4; and

FIG. 6 schematically illustrates an exemplary configuration of anintermediate node within the network of FIG. 1.

DETAILED DESCRIPTION

In the following, for purposes of explanation and not limitation,specific details of the technique are set forth, such as particularsequences of steps, components and configurations, in order to provide athorough understanding of the present disclosure. It will be apparent toa person skilled in the art, that the disclosure may be practiced inother embodiments that depart from these specific details. For example,while the embodiments are described with reference to atelecommunications backhaul network, it will be apparent to a personskilled in the art that the disclosure can also be practiced in thecontext of any other mobile or stationary data network, or a combinationthereof. Furthermore, while the disclosure is primarily described in thecontext of Ethernet OAM according to the Recommendation ITU-T Y.1731 andthe standard document IEEE 802.1ag using continuity check messagesaccording to the protocol defined in the standard document G.8031/Y.1342on Ethernet Linear Protection Switching mechanism, the disclosure mayalso be applied in the context of any other protection switchingmechanism, such as a network using Multiprotocol Label Switching (MPLS)mechanism and/or continuity check messages according to the MPLSTransport Protocol (TP).

Moreover, those skilled in the art will appreciate that services,functions, logic components and steps explained herein may beimplemented using software functioning in conjunction with a programmedmicroprocessor, or using an Application Specific Integrated Circuit(ASIC), a Digital Signal Processor (DSP), or a general purpose computer.It will also be appreciated that, while the following embodiments aredescribed in the context of methods and devices, the technique may alsobe embodied in a computer program product as well as in a systemcomprising a computer processor and a memory coupled to the processor,wherein the memory is encoded with one or more programs configured toexecute the services, functions, logic components or steps disclosedherein.

FIG. 1 shows an exemplary network 100 for practicing the techniquedisclosed herein. The network 100 includes a first end node 102 and asecond end node 104. The first end node 102 and the second end node 104are connected via a first routing path 106 and a second routing path108. The second routing path 108 is different from the first routingpath 106. The first routing path 106 includes at least one anintermediate node 110. The second routing path 108 includes differentintermediate nodes 120 and 130. A functionality provided by each of theintermediate nodes 120 and 130 may correspond to the functionality ofthe intermediate node 110.

The first routing path 106 further includes a plurality of links forconnecting the nodes of the first routing path 106 in a linear topology.Similarly, the second routing path 108 includes a plurality of linksconnecting the end nodes 102 and 104 via the intermediate nodes 120 and130 in a linear topology. In the exemplary network 100, shown in FIG. 1,the first end node 102 is connected to the intermediate node 110 via afiber-optic link 112. The intermediate node 110 is connected to thesecond end node 104 via a microwave link 113.

The topology of the network 100 shown in FIG. 1 is a simplified exampleof a double-connected network. As a variant, the network 100 can includemore than one second routing path 108 for data connection between thefirst end node 102 and the second end node 104.

In the second routing path 108, the first end node 102 is connected tothe intermediate node 120 via a copper cable link 116. The intermediatenode 120 is connected to the intermediate node 130 via a fiber-opticlink 117. The intermediate node 130 is connected to the second end node104 via a microwave link 118. In a variant, the links along one or eachof the first routing path 106 and the second routing path 108 use equalimplementations on a physical layer or implementations deviating fromthose shown in FIG. 1.

FIG. 1 shows a telecommunications backhaul network as an example of thenetwork 100. The first end node 102 includes a serving gate way 122providing a connection 126 to a Public Data Network (PDN). The secondend node 104 includes a base station 124. The base station 124 is awireless connection to a plurality of User Equipments (UEs) 128.Services available by means of the PDN are thus provided to the UEs 128by routing data frames belonging to the different services along thefirst routing path 106 or the second routing path 108. Such servicesinclude voice services and data services.

In more detail, service types can include one or more of Guaranteed BitRate (GBR) voice services, Circuit Emulation Services (CES), highlyavailable Committed Information Rate (CIR) services and Minimum RateStreaming Video services. The GBR voice services have limited toleranceto loss, delay and jitter. Users tolerate only very short time ofoutage. This means that service restoration should be completed within,e.g., 50 ms to avoid termination of the voice session by the user. TheCESs do not tolerate an insufficient bandwidth. In case of insufficientbandwidth, the CESs will collapse. Furthermore, since the CESs typicallycarry voice traffic, the voice requirements, e.g., as to the restorationtime, should be fulfilled. Examples of CIR services include use cases,when the Radio Access Network (RAN) and the mobile telecommunicationsbackhaul network 100 are operated by different operators. For example,the RAN operator can lease a fixed capacity transport pipe from theoperator of the telecommunications backhaul network 100 and usehierarchical scheduling at one of the end nodes for managing itsresource sharing control. If the pipe capacity becomes smaller than thevalue defined in the Service Level Agreement (SLA), the resource sharingcontrol mechanism of the RAN operator will not work properly anymore. Inthe case of the Minimum Rate Streaming Video service, a minimum rate forvideo streams should be guaranteed for user satisfaction. Otherwise, theusers will terminate the service.

The telecommunications backhaul network 100 allows establishing aplurality of tunnels between the first end node 102 and second end node104. Each of the tunnels can be associated to one of the services. Moreprecisely, the tunnel is associated to an instance of a service. Oneservice can require more than one tunnel. The tunnels are associated toone of the routing paths 106 and 108. The end nodes 102 and 104 routedata frames along one of the routing paths 106 and 108 according to theassociation of the tunnel to which the data frame belongs. Changing theassociation between service tunnel and its routing path is also referredto as switching of the tunnel.

Assuming that the first routing path 106 is used as a primary routingpath, a reduction in link capacity at one of the links 112 and 113 alongthe first routing path 106 can be due to a technical failure. Thereduction can also be part of a normal mode of operation, such asAdaptive Modulation (AM). As an example of AM, the microwave links 113and 118 are planned for a small Bit Error Rate (BER) at 114 Mbit/sresulting in an availability of 99.999%. The high availability isachieved using Quadrature Amplitude Modulation with four constellationpoints (4 QAM) as a basic modulation. The bit rate of 114 Mbit/sachieved by using 4 QAM is provided to services with strict Quality ofService (QoS) guarantees, such as voice and GBR services.

In case of good radio conditions, e.g., a low Signal-to-Noise Ratio(SNR) of the radio channel used by the microwave link 113, the AMautomatically changes to a higher modulation level. Since the highermodulation level provides a higher data rate but is not as oftenavailable as the planned basic modulation level according to 4 QAM, theincreased data rate is associated with lower availability. For example,the next higher modulation level provides 233 Mbit/s at an availabilityof 99.995%. The next further modulation level provides 352 Mbit/s at anavailability of 99.99%. A bit rate of 402 Mbit/s is achieved with 99.95%availability. The highest modulation level according to 256 QAM is usedin very good radio conditions and enables the microwave link 113 toprovide a bit rate of 455 Mbit/s with 99.9% availability. The highermodulation levels are used for services without strict serviceguarantees, such as best-effort data services, progressive download,etc.

An exemplary case of reduction in link capacity occurs when the link 113of the first routing path 106 changes to a lower modulation level. Thereduction in link capacity may be necessary to maintain a pre-definedBER as the SNR decreases, e.g., due to precipitation between receivingand sending antennas of the microwave link 113.

Conventional methods of controlling network routing in a network havinga double-connected topology similar to the network 100 include EthernetLinear Protection Switching (ELPS) mechanism according to theRecommendation ITU-T G.8031/Y.1342 by the InternationalTelecommunication Union (ITU) and Automatic Linear Protection Switching(ALPS) mechanism according to the MPLS Transport Protocol (MPLS-TP)defined in specifications of the Internet Engineering Task Force (IETF).Such conventional mechanisms detect only a link failure, which can betoo late for protecting a service that is affected by the reduced linkcapacity.

In an illustrative example of a method of controlling network routing ina network having a topology such as or similar to the network 100, exactinformation is needed about an actual traffic volume for consideringtraffic information in a rerouting decision. Such information abouttraffic can be obtained by using performance monitoring functionsbetween the end nodes 102 and 104, e.g., using loss measurement in aMaintenance Association defined by the end nodes 102 and 104 functioningas Maintenance End Points (MEP).

Both active and passive performance monitoring solutions are available.In case of active monitoring, so-called probe packets are injected intothe network 100 at a source point and a sink point calculates whichpercentage of the probe packets is lost within a measurement period. Incase of passive monitoring, the source point and the sink pointcalculate the incoming and received packets, respectively, and the lossratio can be calculated from the difference. The source point is alsoreferred to as an ingress node and the sink node is also referred to asan egress node, e.g., in the context of MPLS networks according to RFC3031.

However, when traffic information is obtained from a performancemeasurement, at least the following two limitations can be identified insome implementations. First, a timescale of the measurement is often toolong. In order to guarantee a short restoration time, e.g., equal to orless than 50 ms, a traffic loss measurement has to be performed inextremely short periods, which is problematic in itself. In practice,typical periods for the traffic loss measurement vary between 100 ms and1 s, or even longer time. If service tunnel rerouting has to beperformed within, e.g., 50 ms, the measurement period should be, e.g.,approximately 20 ms to 30 ms. During the measurement period, which iseven shorter than the restoration time, it is not possible to getadequate information about the actual traffic situation in the network100. For example, if the modulation level of the link 113 employing AMis changed to a lower modulation level at the end of the n-thmeasurement period, the proper loss can only be detected at the end ofthe (n+1)-th period. To sum up, the timescales required for performancemeasurement and service restoration pose a significant problem, since ameasurement period short enough to comply with the required restorationtime does not result in correct information as to the traffic.Furthermore, a delay will almost always occur due to the predeterminedperiodicity of the measurement, since the traffic loss can be detectedonly in the next measurement period. If the length of the measurementperiod is small, then this “extra” delay is small, but the measurementwill be less accurate. As a consequence, rerouting within, e.g., 50 mscan often not be supported by measurement.

A second limitation associated with performance measurements, relates tolink capacity degradation and traffic overload. Solely based on trafficloss, the end nodes 102 and 104 cannot differentiate between a case ofloss as a consequence of capacity degradation and a case of trafficoverload. Some throughput information can be used in this case, butabove-identified problems as to timescales still persist. There is oftennot enough time to get information for supporting a rerouting within,e.g., 50 ms. This problem is solved by at least some embodiments, sincepart of the rerouting trigger is the Adaptive Modulation downswitch,which indicates that the link capacity is degraded.

Based on the above, it can be concluded that solely relying onperformance measurements does often not provide enough exact informationabout the actual traffic volume so as to support a decision onprotection switching within a restoration time required by at least sometypes of services.

FIG. 2 shows a flowchart of a method 200 of controlling network routingin a network including a first end node and a second end node. The firstand second end nodes are connected or connectable along a first routingpath via at least one link. The network further provides a secondrouting path different from the first routing path. The second routingpath includes the same first and second end nodes. The methods 200 maybe performed in the network 100 shown in FIG. 1. More specifically, themethod 200 can be employed for controlling the network 100. The method200 can be partially or completely implemented in one or allintermediate nodes, such as the intermediate node 110, along the firstrouting path 106. In an extended embodiment of the network 100, themethod is implemented in all intermediate nodes along both the firstrouting path 106 and the one or more second routing path 108.

In a step 210 of the method 200, one or more queues are provided. Eachof the queues serves one or more tunnels along the first routing path106. In a step 220 of the method 200, a switching of the tunnel to thesecond routing path 108 is triggered based on a combination ofinformation as to a queue build-up at the queue serving the tunnel, andinformation as to a link capacity of at least one link along the firstrouting path.

The switching of the tunnel is also referred to as protection switchingor rerouting. The technique allows activating the protection switchingonly if required by link capacity degradation and/or traffic situation.In other words, the technique generates a protection switching triggerbased on the combined link capacity information and queue build-upinformation so that rerouting of a tunnel will be performed only if itis required due to degradation of the services carried by the tunnel.

FIG. 3 schematically illustrates a reduction 300 in link capacity. Thecase of the reduced link capacity is discussed for two scenarios denotedby A and B. The link capacity of the link 113 is reduced from a maximumlink capacity 302 to the current or actual link capacity 304. In thescenario A, the current volume of guaranteed traffic 306 is larger thanthe actual link capacity 304. Consequently, rerouting is necessary,e.g., to protect the service underlying the corresponding tunnel. Incontrast, in scenario B, the traffic volume 308 is less than the actuallink capacity 304. Consequently, rerouting is not needed.

The present disclosure allows avoiding such unnecessary switching of thetunnel from the first routing path 106 to the second routing path 108functioning as a back-up path. The technique does not requireconsideration of explicit traffic information in the rerouting decision.Nonetheless, the technique can be extended using a combined switchingdecision allowing for additional traffic information.

Avoiding the unnecessary switching of tunnels can be extremely importantin the case of frequent but short-length (e.g., temporary) linkdegradations including fast capacity fluctuations that may be caused bymultipath fading. In these cases, the technique allows rerouting to beperformed only if a traffic situation requires it, which results in amore stable network operation, since there is no frequent, unnecessaryswitching of tunnels between the primary path and the backup path. Thefrequent and unnecessary switching is also referred to as “flip-flop”.

FIG. 4 schematically illustrates an embodiment of a device 400 adaptedto perform the method 200. The device 400 has access to or includes atleast one link, such as the links 112 and 113 of the first routing path106 described with reference to FIG. 1 above. The device 400 furtherincludes an intermediate node, e.g., the intermediate node 110 of thefirst routing path 106 described above.

The intermediate node 110 includes one or more queues 402, a unit 404for adaptive modulation and/or detecting a change in the modulationlevel applied for the link 113, and a triggering unit 406. There is onequeue 402 for each of the tunnels, data of which is routed along thefirst routing path 106. In a variant there is no one to one mappingbetween queues and tunnels. One queue can serve several tunnels. Thequeues 402 provide information 408 as to a current queue length and/orthe occurrence of a queue build-up to the triggering unit 406.

For example in case of services with strict guarantees, the queuebuild-up is a very efficient way of detecting the impact on traffic dueto link degradation. Typically, guaranteed services have strict delayand jitter requirements. Consequently, the queue size is small, e.g.,compared to queues that serve Transmission Control Protocol (TCP) flows.When the traffic situation causes an overload then fast queue build-upis detected, which indicates that the impacted service is started to bedegraded. This makes it possible to consider traffic information in theprotection switching decision and to trigger the rerouting of the one ormore impacted tunnels within the required restoration time, e.g., within50 ms.

The unit 404 is in communication 410 with the link 113. In one variantof the embodiment of the device 400, the unit 404 is adapted to controlthe adaptive modulation of the link 113. In particular, the unit 404 isadapted to induce a reduction in link capacity of the link 113 inresponse to a change of channel conditions. In another variant of theembodiment of the device 400, the unit 404 is adapted to detect acurrent modulation level applied by the link 113. In particular, theunit 404 is adapted to detect the reduction 300 in link capacity. In allvariants, the unit 404 provides information 412 as to the link capacityof the link 113 to the triggering unit 406.

The triggering unit 406 is adapted to perform the step 220 of the method200. The triggering unit 406 combines the queue build-up information 408and the link capacity information 412. Based on a result 414 of thecombination, a switching of the tunnel (e.g., away from the firstrouting path 106) is triggered.

Various ways of combining the two pieces 408 and 412 of information canbe implemented in the triggering unit 406. For example, the queuebuild-up information may indicate the presence of an unusually longqueue or an unusually rapidly growing queue. Such indications arecollectively referred to as queue build-up. The link capacityinformation 412 can indicate a case of reduced link capacity, alsoreferred to as link capacity degradation. The case of reduced capacityincludes a transient period during which a lower modulation level isapplied by the link 113. The combination can be a logical conjunction ofthe information 408 indicating that the queue build-up occurs as theinformation 412 indicates the case of reduced link capacity, in whichcase the result 414 of the combined pieces of information 408 and 412includes a trigger for the switching. Otherwise, if no rerouting isnecessary, no result 414 is output.

The intermediate node 110, or the triggering unit 406, inform at leastone of the first end node 102 and the second end node 104 about theresult 414, if rerouting is necessary.

In one embodiment of the device 400, the result is provided as controlmessage. The intermediate node 110 generates a message to carry thererouting trigger to one of the end nodes 102 and 104. Currently, thereis no such standardized message, but for example the extension of theAutomatic Protection Switching message described in Recommendation ITU-TY.1731 or in standard document IEEE 802.1ag could be used for thispurpose. Embodiments based on a control message can be standardized,e.g., for technical compatibility of the intermediate node 110 and endnodes 102, 104.

In another embodiment of the device 400, an active and/or explicitdropping of frames including a connectivity check message is applied forinforming at least one of the first end node 102 and the second end node104. According to the ITU-T Recommendation Y.1731, Continuity CheckMessages (CCMs) are used to verify whether the first routing path 106 isavailable or down between the two end nodes 102 and 104. In case of alink failure, the CCMs are lost. The missing of the CCMs informs one ofthe end nodes 102 and 104 that protection action is needed. Active dropof CCM frames makes it possible to trigger rerouting of impacted tunnelsto the second routing path 108 or any other backup path. This embodimentdoes not directly impact the Y.1731 standard. It requires an extendedoperation of one or more of the intermediate nodes, e.g., theintermediate node 110. The dropping of continuity check messages atintermediate nodes is not limited to CCMs according to the Y.1731standard. Any kind of continuity check messages, e.g., messagesexchanged for detecting failure in MPLS networks, can be used as well.Details on actively dropping continuity check messages are also providedin provisional application US 61/560,551.

The triggering unit 406 thus provides the result 414 of the combinedpieces 408 and 412 of information to the end node 102 and/or 104. Theend node 102 and/or 104 explicitly or implicitly receives the result414. In one implementation of queue build-up detection, the triggeringunit 106 provides the result 414 immediately and the receiving end node102 and/or 104 effects the switching of the tunnel immediately. Inanother implementation of queue build-up detection, the switching of thetunnel is delayed. During the delay the queue at which the queuebuild-up has occurred is monitored. If the queue build-up persistsduring the delay, the switching is triggered. The first-mentionedimplementation can be considered as a simpler implementation compared tothe second-mentioned implementation. The second-mentioned implementationcan prevent rapidly switching back and forth between the routing paths106 and 108.

FIG. 5 schematically illustrates further details of the queues 402. Thequeues 402 include a first queue 502, a second queue 504, and a thirdqueue 506. Each of the queues 502 to 506 provides the functionality of aFirst In-First Our (FIFO) buffer. The intermediate node 110 furtherincludes a scheduler 508 adapted to multiplex the queues 502 to 506 tothe link 113. An output of each of the queues 502 to 506 is coupled tothe scheduler 508. The scheduler reads from the output of the queues 502to 506 according to a Round-Robin scheme. Frames stored in the queues502 to 506 are denoted by reference signs of the format xxx-y in FIG. 5,wherein the number “y” indicates the order of read-out for a givenqueue. In each time step of the time-sharing applied by the scheduler508, one of the frames 510-1, 512-1 or 514-1 is read depending on whichof the queues 502 to 506 is processed in the current time step accordingto the Round-Robin scheme.

Thresholds 516 and 518 are setup for the queues 502 and 504,respectively. If the queue length of the one or more queues 502, 504serving at least one impacted tunnel exceeds its queue threshold 516 or518 during a case of link degradation, the result 414 indicates that theat least one impacted service is started to be degraded.

In the situation show in FIG. 5, the first queue 502 has a queue lengthbelow the threshold 516 that is associated to the first queue 502. Thesecond queue 504 has a queue length exceeding its queue threshold 518 asa fourth frame 512-4 is input into the second queue 504. In thissituation, the triggering unit 406 triggers the rerouting so as toswitch the at least one impacted tunnel to the second routing path 108functioning as the backup path. In case of more than one backup path,the rerouting one of the end nodes 102 and 104 further decides uponwhich of the plurality of backup paths takes the role of the secondrouting path 108.

In the first-mentioned implementation of queue build-up detection, thererouting action is triggered immediately when the queue threshold isviolated. In the second-mentioned implementation of queue build-updetection, a timer is started when the queue threshold is violated. Ifduring a given time period T the queue length remains larger than thethreshold, the rerouting action is triggered immediately. Thesecond-mentioned implementation causes some delay in the detection butcan avoid rerouting, if the link capacity degradation can be managed byqueuing in case of the current traffic situation, e.g., in case of atransient congestion or an overload due to a transmission burst.

FIG. 6 schematically illustrates further details of performing themethod 200 by means of the intermediate node 110. The detection ofservice degradation is based on a local and temporally coincidence ofthe queue build-up and the case of link capacity degradation in thenetwork 100.

The end nodes 102 and 104 define a Maintenance Association (MA) and arereferred to as Maintenance End Points (MEPs). The example of the network100 shown in FIG. 6 further includes Maintenance Intermediate Points(MIPs) 109 and 110, each of which implements the functionality of theintermediate node 110 described above. The MIPs are also referred to asManagement Intermediate Points.

The first routing path 106 includes the MEPs 102 and 104, the MIPs 109and 110 between the MEPs 102 and 104, and a plurality of links 111, 112,113 arranged to linearly connect the nodes 102, 109, 110, 104. Thenetwork 100 further provides a second routing path 108 including thesame MEPs 102 and 104, different MIPs 120 and 130 providing thefunctionality of the intermediate node 110 described above, and aplurality of links 116, 117, 118 connecting the nodes 102, 120, 130, 104along the second routing path 108.

Each intermediate node 109 and 110 along the first routing path 106(functioning as primary routing path) includes a table 600. The table600 contains information as to which tunnels indicated in a column 604should be rerouted in case of a given link capacity indicated in acolumn 602. The column 602 thus defines a minimum link capacity. Thetable 600 further allows determining which one or more queues indicatedin a column 606 serve the one or more services carried by the giventunnel indicated in the column 604, as can be seen in FIG. 6.

If the microwave link capacity is switched to a certain value, theimpacted MIP node 110 checks its table 600. If there is an entry orentries for the current link capacity (e.g., a minimum link capacitythat is equal to or higher than the current link capacity), the impactedor associated one or more tunnels are identified and the actual queuelength of the one or more queues, which serve frames belonging to thetunnels, are started to be monitored.

If the queue threshold 518 of the queue 540 is not violated, the MIPnode 110 does not do any (triggering) action. The traffic, e.g.,including the tunnels “Tunnel_1” and “Tunnel_2”, is kept on the primarypath 106.

The queue build-up is checked continuously while the microwave link 113is degraded. If the actual length of the queue 504 becomes larger thanthe threshold 518, congestion is detected and degradation of the servicecarried by the tunnel “Tunnel_1” is assumed, since it seems that thereis not enough capacity to carry the traffic of the tunnel “Tunnel_1”.Then, the MIP 110 informs the MEP 104 that rerouting is necessary.Examples on implicitly or explicitly providing the information totrigger the rerouting have been described above.

The first column 602 of the table 600 indicates the minimum linkcapacity for routing the tunnel identified by the tunnel identifier‘Tunnel_id” included in the second column 604 of the corresponding lineof the table 600. The queue associated to the corresponding tunnel isindicated in the third column 606 of the table 600.

In an extended embodiment of the method 200 and the intermediate node110, a back-rerouting or back-switching of the tunnel “Tunnel_1” fromthe backup path 108 to the primary path 106 can be performed, if thedegraded link capacity (e.g., below 233 Mbps) is increased to therequired value (e.g., above 233 Mbps) and if this link capacity remainsstable for a given time. In the extended embodiment, the flip-flopbetween the primary path 106 and the secondary paths 108 can be avoided.In some implementations, a drawback of the extended embodiment could bethat traffic awareness is lost in the tunnel back-switching. Even if theprimary tunnel (i.e., the tunnel “Tunnel_1” routed along the primarypath 106) could serve the traffic, the “Tunnel_1” is kept on thesecondary path 108, until the link 113 is changed to a higher capacityon the primary path 106 (e.g., by AM switching up the link 113 to ahigher modulation level).

As has become apparent from the above exemplary embodiments, at leastsome of the embodiments realize a protection switching mechanism that isperformed for one or more impacted tunnels only if a traffic situationrequires the switching. If the current traffic volume can be handled bythe available (degraded) link capacity, the traffic is kept on theprimary path. Same or other embodiments provide that unnecessaryrerouting and/or frequent switching between primary and backup paths canbe avoided. Latter is important in cases of frequent but short-term linkdegradation, e.g., due to multipath fading.

At least some implementations can achieve a short restoration time.E.g., some embodiments can perform rerouting within 50 ms.

Certain implementations do not require amendments at edge nodes (e.g.,at Maintenance End Points) in the course of the implementation and/or donot require non-standardized features at the edge nodes. In same or someother implementations, the Maintenance Intermediate Points shouldsupport the triggering of the rerouting based on a queue build-up.

The technique can even be applied in case of complex topologies and/ormulti-edge networks. At least in some implementations, there is noimpact on an operation if the degraded tunnels are handled by differentedge nodes, e.g., different Maintenance End Points. In same or someother implementations, there is no impact on the operation, if backuppaths of the tunnels are different.

The technique can be implemented independent of a network technology.The technique can be generalized and/or used independent from thenetwork technology. The technique can be implemented with any kind ofalternatives as to how an end node is informed about the necessity ofrerouting.

1-25. (canceled)
 26. A method of controlling network routing in anetwork including a first end node and a second end node connectablealong a first routing path via at least one link, wherein the networkincludes at least one intermediate node along the first routing pathbetween the end nodes, the network further providing a second routingpath including the first end node and the second end node, the methodcomprising: providing one or more queues, each of which serves at leastone tunnel along the first routing path, wherein the one or more queuesare associated to one of the at least one intermediate node along thefirst routing path; and triggering a switching of at least a portion ofthe at least one tunnel to the second routing path based on acombination of information as to a queue build-up at the queue servingthe tunnel and information as to a link capacity of at least one of thelinks of the first routing path.
 27. The method of claim 26, wherein theinformation as to the queue build-up is obtained by checking a queuelength.
 28. The method of claim 26, wherein a queue threshold is set foreach of the one or more queues.
 29. The method of claim 28, wherein theswitching of the tunnel is triggered when a queue length of the queueserving the tunnel exceeds the respective queue threshold.
 30. Themethod of claim 26, wherein the switching is triggered during a case ofreduced link capacity of the at least one of the links of the firstrouting path.
 31. The method of claim 30, wherein the queue build-up ischecked continuously while the link capacity remains reduced.
 32. Themethod of claim 26, wherein a reduction in the link capacity ismonitored while the information indicates the queue build-up.
 33. Themethod of claim 26, wherein at least one of the queue build-upinformation and the link capacity information is generated or availableat the intermediate node.
 34. The method of claim 26, wherein the queuebuild-up information and the link capacity information are combined atthe intermediate node.
 35. The method of claim 26, wherein theintermediate node triggers the switching by informing at least one ofthe end nodes as to the switching of the tunnel.
 36. The method of claim26, wherein the intermediate node triggers the switching by generating acontrol message and providing the control message to at least one of theend nodes.
 37. The method of claim 26, wherein the intermediate nodetriggers the switching by dropping data frames including a connectivitycheck message.
 38. The method of claim 26, wherein a plurality of queuesis provided at the intermediate node and controlled by a scheduler ofthe intermediate node.
 39. The method of claim 26, wherein each of theat least one intermediate node along the first routing path includes atable containing information as to which of the tunnels is to beswitched in case of a given link capacity.
 40. The method of claim 39,wherein the table associates a queue to a given tunnel.
 41. The methodof claim 39, wherein the table associates a minimum link capacity to agiven tunnel.
 42. The method of claim 26, wherein the switching istriggered immediately when the information indicates the queue build-up.43. The method of claim 26, wherein the triggering of the switchingincludes starting a timer, the switching being further subject to thequeue build-up remaining until the timer expires.
 44. The method ofclaim 26, wherein the switched tunnel is switched back from the secondrouting path to the first routing path when the link capacity fulfillsfor a certain time a minimum link capacity associated to the switchedtunnel.
 45. The method of claim 26, wherein the at least one link alongthe first routing path includes a microwave link.
 46. The method ofclaim 26, wherein the network is a telecommunications backhaul network.47. A computer-readable recording medium storing a computer programproduct comprising program code portions that, when executed by aprocessor in a device, configures the device to: provide one or morequeues, each of which serves at least one tunnel along a first routingpath that includes one or more links and further includes at least oneintermediate node between first and second end nodes, wherein the firstand second end nodes are further interconnected by one or more linksalong a second routing path that includes one or more links and one ormore intermediate nodes; and trigger a switching of at least a portionof the at least one tunnel to the second routing path, based on acombination of information as to a queue build-up at the queue servingthe tunnel and information as to a link capacity of at least one of thelinks of the first routing path.
 48. A device for controlling networkrouting in a network including a first end node and a second end nodeconnectable along a first routing path via at least one link, whereinthe network includes at least one intermediate node along the firstrouting path between the end nodes, the network further providing asecond routing path including the first end node and the second endnode, the device being adapted to: provide one or more queues, each ofwhich serves at least one tunnel along the first routing path, whereinthe one or more queues are associated to one of the at least oneintermediate node along the first routing path; and trigger a switchingof at least a portion of the at least one tunnel to the second routingpath based on a combination of information as to a queue build-up at thequeue serving the tunnel and information as to a link capacity of atleast one of the links of the first routing path.
 49. A networkcomprising: a first end node and a second end node connectable along afirst routing path via at least one link, wherein the network includesat least one intermediate node along the first routing path between theend nodes, wherein the network further provides a second routing pathincluding the first end node and the second end node; and a deviceconfigured to: provide one or more queues, each of which serves at leastone tunnel along the first routing path, wherein the one or more queuesare associated to one of the at least one intermediate node along thefirst routing path; and trigger a switching of at least a portion of theat least one tunnel to the second routing path, based on a combinationof information as to a queue build-up at the queue serving the tunneland information as to a link capacity of at least one of the links ofthe first routing path.